KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 43. N:o 10. lg 
cipal rifts or ramifications of the Milky Way seem, at a closer examination, not to 
be understood otherwise than as real rifts in an originally integral body of gaseous 
matter, thoroughly as rifts arise, owing to stresses, in the common atmospheric clouds. 
The strain which once produced the great ramification of the Milky Way must, on 
these hypothesis, have been directed vertically to both sides of the great circle of 
the Milky Way, and it becomes thus at once very probable that its cause is to be 
searched for in the breaking down at its poles of a great spheroidical shell of matter, 
which originally formed the body of the Galaxy. In fact, of the mechanical conse- 
quences of such a transformation are to be noted: possible rifts in the remaining 
equatorial regions on account of loss of continuity along certain lines of least den- 
sity; furthermore obstructed parts of the polar regions, which may have resulted in 
the groups of spiral nebulze', at present observed arround the poles of the Galaxy. 
It is very clear, indeed, that the matter in such a shell should possess a higher 
degree of conservative coherence at its equator than at its poles, where no supporting 
force balances the gravity, as soon as the inner substance of the body begins to 
condense into clustering parts. Analogies to the supposed diversity of matter at the 
poles and at the equator of such a shell are furnished by the wellknown features of 
solar rotation at the Suns equator and at its poles. 
The hypothesis, thus formed on the original state of the Galaxy, receives an im- 
portant support by the actual view according to which some of the planetary ne- 
bule may be bodies whose substantial state is that of a luminous shell of 
matter. According to my opinion, the breaking down at the poles of the nebulzre 
has in most cases taken place, leaving as a fragment a substantially cylindrical 
equatorial ring, the products, supposed to exist at the poles, being invisible on ac- 
count of their comparatively faint luminosity. A striking example of this fact is 
afforded by the Dumbbell Nebula G. C. 4532, in which the process of breaking down 
at the poles seems to be actually going on. 
8. Distribution of planetary nebulce. 
One finds sometimes the assertion that the planetary nebulze are situated in the 
Milky Way or near it. This view is for instance expressed by CLEVELAND ÅBBE. 
In his memoir, referred to above, he asserts that the planetary nebulx may be classed 
with the Clusters as regards their arrangement and distance from us, and are to be 
considered as the gaseous globes belonging to our Via Lactea. PROCTOR does not 
partake of this view, for in his study, referred to above, he only maintains that the 
irregular gaseous nebul&e are all on or close to the Milky Way, except one etc. Even 
WATERS expresses himself on the subject in a somewhat undecided manner, in obser- 
ving that the complete segregation of all the nebulze (the gaseous nebulzxe excepted) 
! The recent determination of the parallax of the Andromeda-nebula [Astron. iaktt. och unders. Bd 8 
N:o 4] affords an additional proof of the connexion of spiral nebulx with the stars system. 
K. Sv. Vet. Akad. Handl. Band 43. N:o 10. 
